An optical scanning observation apparatus that scans a beam of light from the end of an optical fiber over an object and detects light that is reflected, scattered, or the like by the object or detects fluorescent light or the like generated by the object is known (for example, see patent literature (PTL) 1). For such an apparatus to scan the irradiated light over the object, an end of the optical fiber is supported to allow oscillation of the tip where light is emitted, and the optical fiber is vibrated by disposing a piezoelectric element near the support.
Typical known methods of scanning an optical fiber include spiral scanning, in which the spot of irradiated light is scanned to trace a spiral, and raster scanning, in which the optical fiber is vibrated at high speed in one direction while being moved in an orthogonal direction at low speed. In a typical spiral scanning pattern, the vibration frequency is set to the resonance frequency. During raster scanning, the optical fiber is preferably vibrated at the resonance frequency in the direction of vibration at high speed. Therefore, the fiber has been driven to vibrate on the basis of the resonance frequency that is determined by the design values of the optical scanning observation apparatus.